Project Summary/Abstract Primary hyperparathyroidism (PHPT) is a common endocrine disorder that predominantly affects patients older than 60 and is increasing in prevalence. Population-based data on long-term outcomes for geriatric patients who undergo parathyroidectomy or observation with medical management are lacking. Understanding which older adults will benefit from medical vs. surgical management will help reduce the burden of the late complications of PHPT, without exposing elders who will not benefit to the risks of surgery. Our long-term goal is to devise evidence-based guidelines to optimally manage older adults with PHPT with parathyroidectomy or medical therapy to reduce morbidity, functional and cognitive decline, and mortality. The overall objective of this proposed study is to quantify the impact of parathyroidectomy on the risk of subsequent fracture and major adverse cardiovascular (CV) events in older adults with PHPT, and to identify risk factors for morbidity with medical and surgical management. Our central hypothesis is that older adults with PHPT who undergo parathyroidectomy experience fewer fractures and major adverse CV events than those who do not undergo surgery, and that patient factors associated with adverse outcomes in both treatment groups can be identified and used to guide patient selection for surgery. This hypothesis will be tested using longitudinal analysis of Medicare claims data to identify a nationally representative cohort of patients with PHPT and a control cohort without PHPT to pursue two specific aims: 1) Identify factors associated with the surgical management of PHPT in older adults in the United States; and 2) Compare the 5-year incidence of and risk factors for new fractures or major adverse CV events in older adults with PHPT undergoing parathyroidectomy vs. medical management and determine the relationship between patient characteristics and adverse outcomes. This project is innovative because it will be the first study to examine the long-term outcomes of parathyroidectomy vs. medical management for PHPT in a national population older than 65 in the United States, and the first study to look at the management of PHPT in Medicare beneficiaries. The proposed research is significant because it will provide benchmark data on the long-term outcomes for geriatric patients with PHPT who undergo parathyroidectomy vs. medical management and greatly enhance our understanding of geriatric- specific predictors of adverse outcomes in the management of PHPT.